Solid oxide fuel cell ("SOFC") systems, which convert potential chemical energy from reactant gases into electrical energy, are well known in the art. See e.g., P.C.T. Patent Application PCT/US95/01404 to Elangovan et al., (published 1995). Fuel cell plates, having anode and cathode surfaces, are positioned parallel one another in stacks, separated by interconnectors having channels for air and gas flow. A fuel gas, such as H.sub.2, CO, CH.sub.4 or other hydrocarbon-containing gas, is fed through channels to the anode surfaces of the fuel cells. An air stream confining oxygen is fed in separate channels, typically orthogonal to the fuel gas channels, to the cathode surfaces of the fuel cells. An electrical current may be obtained by electrically connecting the anode and cathode due to the current flux of electrons involved in the electrochemical reaction.
The air stream must be pre-heated to prevent the cooling of the electrolyte plates below the operating temperature, typically between 800.degree.-1000.degree. C. SOFC systems employing various designs of heat exchangers, which transfer heat from the exhaust air stream to the incoming air stream, have been developed. See e.g., U.S. Pat. No. 5,340,664 to Hartvigsen, (Aug. 23, 1994), which is hereby incorporated herein in its entirety by reference.
Previously, SOFC systems utilizing heat exchangers have been hampered by extensive ducting and insulation requirements. Generally, the incoming air stream, after exiting the heat exchanger, is transferred through heavily insulated ductwork to a central air plenum where it is fed through the desired fuel cell stacks. Such ductwork and insulation requirements reduce the efficiency of the heat exchange system and increase the weight and cost of the SOFC system. The heat exchange plumbing also reduces the integrity of the supporting structural foundation and limits the fuel cell design configurations. In addition, manufacturing and fabrication of such systems is often difficult and costly. The heat exchange plumbing systems also make stack installation and system monitoring both difficult and inconvenient.
In view of the foregoing, a high-efficiency fuel cell module employing a heat exchanger, while reducing the necessary hardware and insulation requirements and facilitating accessibility, monitoring, fabrication and design variation, without compromising the structural integrity of the support, would be highly desirable.